The present invention is directed to color switches, and, in particular, to color switches based on molecules including rotor and stator components as part of their structure.
Switching molecules capable of changing color from one state to another under the influence of an electric field are the subject of ongoing investigation. In general, the color change occurs through a molecular conformation change that alters the degree of electron conjugation across the molecule and, thereby, its molecular orbital-induced HOMO-LUMO (highest occupied molecular orbitalxe2x80x94lowest unoccupied molecular orbital) states. In one particular embodiment, the conformation change occurs through the field rotation of a ring or rings within the molecule. In this instance, the conjugation is broken between the rotating rings, called rotors, and ring structures that do not rotate, called stators. The rotors have electric dipoles that induce rotation within a given field. A coupling group (e.g., acetylene) between the rotor and stator elements serves as a xe2x80x9cbearingxe2x80x9d and conjugation bridge between the rotor and stator.
The novel molecular color switch promises a unique set of dye-like optical properties that make it ideal for applications such as electronic paper, paper-like displays, electronic books, projection displays and the like.
A major challenge in the development of the molecular color switch is the need for self-assembled colorant layers on the order of 0.05 to 1.0 micrometer in thickness. Each switch molecule in the colorant layer used in print or display media must be correctly oriented with respect to the switching field and be spaced sufficiently from other molecules to allow unhindered rotation of the switching rotors. Such spacing and alignment must be repeated over a colorant thickness sufficient to achieve the optical density typical of commercial print (nominally 0.5 to 1.0 micrometer). A related challenge is to design the colorant layer for cost-effective switching voltages and addressing. Yet another challenge is to design a colorant layer that switches from a highly conjugated black to transparent state under such low switching voltages. A still further challenge is to design a means to constrain the stator sections of the molecular switch to prevent rotation with rotor rotation. The lowest conformational energy state of the typical molecular switch provides for planar rotors and stators. Unconstrained, the rotor and stator will naturally want to rotate together, vitiating any desired color change. Yet another challenge is to design a colorant layer that provides high optical density with minimized switching voltage. Still further, there is the challenge of providing a means for creating specific subtractive colors, such as cyan, magenta and yellow meeting the above rotor orientation and switching voltage needs. Further yet, there is the challenge of providing a means for bi-stable color switching enabling the colored and transparent states to remain stable indefinitely in the absence of a field. Bi-stable operation enables such applications as electronic paper and electronic books. It also provides the lowest energy alternative for display related applications since no holding voltage is required to maintain a pixel and only pixels needing to change are switched.
In the foregoing applications, a general stator constraint and molecule spacing scheme involving bulky side groups on stators has been described. Such bulky groups might include attachment of one or more carbon tetrahedrons having three phenyl rings, for example. This approach, however, has been found to have some drawbacks. Most notably, such bulky groups have large interstitial spaces that do not provide inter-molecular spacing function, allowing the potential that adjacent molecules may be poorly spaced. For the same reason, the bulky side groups do not inherently guarantee molecule alignment with the field and likely inhibit field-induced alignment during colorant film formation. Furthermore, the above-referenced applications do not provide chemistry specific to optically thick colorant films nor bi-stable switch operation.
Thus, there is a need to provide thin molecular films having an electric field switchable color, providing print-like optical density at low switching voltage.
In accordance with the embodiments disclosed herein, a selfassembled molecular color switch comprising coupled coaxial rotors and non-coaxial stators, with each rotor rotatably connected to two stators with a connector, to form a plurality of spaced molecular planes of interconnected polygon cells, wherein all rotors at rest are parallel and orthogonal to an electric field.